Disasters, man made or otherwise aren't just likely but will happen, but as to the eradication of our species and knowledge, right now there is very little that would ultimately do that, barring a super nova in our vicinity. There is every reason to believe that at least a portion of humanity would survive just about every forseeable scenario. That doesn't mean that our growth as a species wouldn't be impacted or stunted for a while, it would be, eradicated, no. That's sort of like saying anyone that survived such an event, for no reason in particular, would revert to living in mud huts and utilizing only stone age techniques and completely shun the knowledge we have in perpetuity.
As to that applying to the Drake equation, it's likely that any other civilization also went thru this sort of period, but even in spite of disasters, self made or natural, survived it. Could we make this harder on ourselves, or in the case of another civilization could they have made this harder on themselves, absolutely. However, I find it extremely unlikely that in either case a species would self eradicate, to include our own, even potentially in spite of ourselves. A bad actor or actors could certainly do a lot of damage, but there is nothing to suggest they could eradicate the planet, not even close.
The more likely reality is that we are looking for the wrong signatures, simply because we don't understand them yet. You don't use a rotary phone anymore, no one has in years, yet in searching the cosmos, that's sort of like what we are doing, because for now, that's what we know.